Characterization of Entamoeba histolytica alpha-actinin2.

We have cloned and characterized a second alpha-actinin isoform in Entamoeba histolytica. This protein, alpha-actinin2, has a N-terminal actin-binding domain, a C-terminal calcium-binding domain and an intervening rod domain containing two spectrin repeats. The protein binds and cross-links actin filaments in a calcium-dependent manner. Therefore alpha-actinin2 is a genuine alpha-actinin except for the shorter rod domain compared to the rod domain of isoforms of higher organisms. A alpha-actinin-like protein has previous been implicated in the adherence to the host cell and infection. It is therefore possible that alpha-actinin2 is involved in mechanism of infection, and in particular in reorganisation of the parasite's cytoskeleton that follows on adherence. E. histolytica alpha-actinin2 represents one of the first members of the spectrin superfamily where well defined spectrin repeats are found. The isolation and characterization of this second alpha-actinin isoform is valuable not only into the study of E. histolytica infection mechanisms, but also for understanding the evolution processes of the spectrin superfamily.